Masimo Rad-G Pulse Oximeter
I’ve long been a fan of the pulse oximeters produced by Masimo (Irvine, California). Please see my article from Contemporary Pediatrics October 2014, Pulse oximetry: The fifth vital sign, for a discussion of the history of pulse oximetry, review of the technology, and tips for using pulse oximeters.
An oximetry sensor consists of red and infrared light emitting diodes and a photodetector placed on opposite sides of a measurement site, usually the finger in adults and children but the palm or foot in neonates and toddlers. The ratio of red to infrared light that passes through the tissue depends on the percentage of oxygenated versus deoxygenated hemoglobin in the arterial circulation of the tissue. In turn, the percentage of oxygen saturation displayed by a pulse oximeter is determined by an algorithm in the microprocessor of the device based on saturation measurements obtained by sampling a large population of patients breathing mixtures of decreased oxygen concentrations. These algorithms are unique for each manufacturer. Pulse oximeters take hundreds of readings over a 3- to 6-second time period and update their measurements every 0.5 to 1 second. In the best of circumstances, pulse oximeter readings come within 2% to 3% of those produced by co-oximetry, the measurement of arterial blood directly by a blood gas analyzer.
When using oxygen saturation clinically, it is important to recall the oxygen dissociation curve we learned in medical school . The upper “bend” in the oxygen dissociation curve occurs at a pO2 of 60 mm Hg of oxygen, which corresponds to an oxygen saturation of 90%. Therefore, one needs to be aware that saturation levels of 90% and below are associated with hypoxemia.
Masimo uses a proprietary technology called “signal extraction technology” (SET), which provides rapid signal acquisition and signal stability even when used in the “wiggly’ patients pediatricians deal with every day. I have been using the Masimo Rad-G pulse oximeter for some time. It features a touch screen interface, is very durable, and provides readings of pulse oximetry, wave form, perfusion index, as well as a respiration rate from a photoplethysmogram. Best of all there is a new pediatric sensor that is now available for children 10 kg and above which makes it easy to obtain reading in young patients.